1. Field of the Invention
The present invention relates to a L-ascorbic acid derivative having an improved water-in-stability and a method for preparation thereof, and to a skin-whitening cosmetic composition containing the same as an active ingredient.
2. Related Arts
L-ascorbic acid has a strong anti-oxidation activity, promoting biosynthesis of collagen and proliferation of fibroblast. Especially, it is very effective in inhibiting melanin-formation and thereby can be employed in topical applications for purpose of preventing an abnormal pigmentation such as freckle.
However, ascorbic acid is easily decomposed by oxidation in an aqueous base to cause a reduction of activity during long-term storage.
Under this circumstance, the recent studies have been conducted to provide a new derivative which is stable in an aqueous base. The proposed derivatives are in the form of ester obtained by esterification of 2-, 3-, 5- or 6-position hydroxyl group of L-ascorbic acid with phosphoric or sulfuric group or fatty acid such as stearic acid and palmitic acid. The ester bond of these derivatives can be easily decomposed by a hydrolytic enzyme to release L-ascorbic acid and thereby provide effective physiological actions of L-ascorbic acid. For example, there is ascorbic acid 2-phosphate magnesium. This compound can be easily percutaneously penetrated by introduction of phosphoric group to deliver L-ascorbic acid to corium layer, as well as is itself very stable in an aqueous base without any discoloration by oxidation. So, this compound has been proposed as an active ingredient for skin-whitening cosmetic compositions (JP 1-283208A, JP 3-227907A).
However, although ascorbic acid 2-phosphate magnesium has some improvement in stability of itself, it has drawbacks in forming insoluble crystals by itself or precipitates with other ingredients such as anionic polymers and surfactants in an aqueous base. This precipitation is supposed to be due to low solubility in water.
Recently, ascorbic acid-2-O-.alpha.-glucoside has been proposed as a new material not having any above problem or drawback. This derivative is produced by fermentation. However, up to now, its percutaneous penetration or action for inhibiting melanin-formation are uncertain. In addition, it is very expensive because it is provided by fermentation.
Therefore, the present inventors have conducted extensive studies in order to provide a new derivative which itself is very stable and does not cause any precipitation in an aqueous base. They made efforts to find phosphoric group to be bonded to 2-hydroxyl group of L-ascorbic acid. As this phosphoric group, they considered 3-aminopropane phosphoric acid which has a good solubility in water to be employed in any type cosmetic compositions as far as they contain some water. That is to say, they introduced 3-aminopropane phosphoric acid into 2-hydroxyl group of L-ascorbic acid by phosphoric ester bond, to produce 2-(3-aminopropane phosphoric acid)-L-ascorbate.
Especially, 3-aminopropane phosphoric acid itself is active cosmetic material which can increase moisture retention ability, recuperation ability against the metamorphosis and firmness, of the skin, thereby deferring a skin aging effectively. In addition, it does not cause skin irritation and is stable to be easily formulated into the cosmetic products, as well as can promote cell-growth and biosynthesis of the epidermal collagen. Based on these effects and actions, cosmetic compositions containing 3-aminopropane phosphoric acid has been proposed in U.S. Pat. No. 5,723,645.
The present inventors confirmed that 2-(3-aminopropane phosphoric acid)-L-ascorbate itself is very stable without any discoloration and reduction of activity by oxidation and does not cause any precipitation in an aqueous base. Further, since this derivative can be easily percutaneously penetrated by phosphoric group, and once absorbed can be easily decomposed by a hydrolytic enzyme to release ascorbic acid and 3-aminopropane phosphoric acid, it is expected that a cosmetic composition containing this derivative can provide effective physiological actions onto the skin of both of L-ascorbic acid and 3-aminopropane phosphoric acid. Based on this expectation, the present invention has been completed.